If I'm honest, I would watch two towers sooner than I would the other two simply because of the immense battle scene that the movie is centered around, but the other two have more plot value, so I would rate them higher as films.

Star Wars:

1. Empire Strikes Back
2. Return of the Jedi
3. A New Hope
4. Attack of the Clones
5. The Phantom Menace
6. Revenge of the Sith

The first three are straight forward on this, but Attack of the Clones gets a higher spot for the newer ones because it gave me what I wanted to see, a huge fight between the jedi and the androids. Of course Phantom Menace is five then because, well, Liam Neeson. And Revenge of the Sith wasn't too bad, but it was, in my eyes, the worst of them all.